L. E. Robinson and J. Davidson 
of this tick conform to the general rule which obtains in the Arthro- 
poda, namely, that they are all, including the visceral muscles, of the 
transversely striated type. Later observers have usually confined their 
attention to the musculature of the mouth-parts and pharynx, the 
remainder of the muscular system receiving only casual treatment. 
A short historical resumd of the subject is to be found in Bonnet’s work 
on the comparative anatomy and development of the Ixodoidea 1 . 
The exception referred to above, is the work of Nordenskiold on the 
histology of the body-muscles of Ixodes ricinus 2 . He calls attention to 
the existence of a most remarkable feature in the structure of the dorso- 
ventral body-muscles, which provides for the relatively great increase in 
length of these muscle columns necessarily accompanying the process of 
engorgement. In Argas persicus, as might be expected from its different 
mode of life, this exceptional structure of the body muscles, as seen in 
Ixodes, is entirely absent, or only exists in a modified form and to a 
limited extent, during those phases of the tick’s existence in which 
histiogenetic changes are following the dissolution of the tissues which 
precedes each moult. 
So far as we have been able to see, the only marked difference 
between the body-muscles and the muscles of the appendages in Argas 
persicus is that to which Heller calls attention, viz. that the former are 
muscle columns which maintain a practically constant diameter from 
one extremity to the other, and are inserted into the chitinous integu¬ 
ment without the intermedium of a tendon. As will be shown later, 
the latter difference is unimportant, inasmuch as a careful examination 
of the insertions of these muscles shows that Heller’s view was not 
strictly correct. 
The following description of the histological structure of the muscles 
of Argas persicus applies equally to both the dorso-ventral body-muscles 
and to the muscles of the appendages. 
Each muscle is composed of a number of parallel fibres, the cross 
section of which presents a more or less polygonal figure, due to mutual 
pressure. The fibres are interpenetrated by a delicate connective tissue 
framework which, on the external surface of the muscle, forms an in¬ 
vesting sheath, but is of so flimsy a nature that it does not suffice to 
hold the muscle fibres together when the surrounding parts are disturbed, 
with the result that in dissections, the fibres are apt to become widely 
separated at the torn extremities of the muscles. In sections, also, the 
component fibres of a muscle are often more or less separated on account 
1 Bonnet, A. (1907), pp. 96, 97. 2 Nordenskiold, E. (1908), p. 670. 
25—2 
